Tunneling metamagnetic resistance memory device and methods of operating the same

ABSTRACT

A magnetoresistive memory device includes a first electrode, a second electrode, and a layer stack located between the first electrode and the second electrode. The layer stack may include a ferroelectric material layer and a metamagnetic tunnel junction containing a metamagnetic material layer, an insulating barrier layer, and a metallic material layer. Alternatively, the layer stack may include a multiferroic material layer, the metamagnetic material layer, the insulating barrier layer, and a reference magnetization layer.

FIELD

The present disclosure relates generally to the field ofmagnetoresistive memory devices and specifically to tunnelingmetamagnetic resistance memory devices employing electricalfield-induced switching and methods of operating the same.

BACKGROUND

A magnetoresistive memory device can store information employing thedifference in electrical resistance of a first configuration in which afree magnetization layer has a magnetization direction that is parallelto the magnetization of a reference magnetization layer and a secondconfiguration in which the free magnetization layer has a magnetizationdirection that is antiparallel to the magnetization of the referencemagnetization layer. Programming of the magnetoresistive memory device,such as a STT-MRAM, typically involves flipping of the direction of themagnetization of the free layer employing an external power source usinga tunneling current through a magnetic tunnel junction. However, theswitching power required to generate the tunneling current is higherthan desired.

SUMMARY

According to an aspect of the present disclosure, a magnetoresistivememory device includes a first electrode, a second electrode and a layerstack located between the first electrode and the second electrode, thelayer stack comprising a ferroelectric material layer and a metamagnetictunnel junction. The metamagnetic tunnel junction comprises ametamagnetic material layer, a metallic material layer, and aninsulating barrier layer between the metallic material layer and themetamagnetic material layer.

According to another aspect of the present disclosure, amagnetoresistive memory device includes a first electrode, a secondelectrode, and a layer stack located between the first electrode and thesecond electrode, the layer stack comprising a multiferroic materiallayer and a metamagnetic tunnel junction. The metamagnetic tunneljunction comprises a metamagnetic material layer, a referencemagnetization layer, and an insulating barrier layer between thereference magnetization layer and the metamagnetic material layer.

According to still another aspect of the present disclosure, a method ofoperating any magnetoresistive memory device of the present disclosureis provided, which comprises: applying a first polarity programmingvoltage to the first electrode relative to the second electrode in afirst programming step to switch a state of the metamagnetic materiallayer from the non-magnetic state to the magnetic state; and applying asecond polarity programming voltage having an opposite polarity of thefirst polarity programming voltage the first electrode relative to thesecond electrode in a second programming step to switch the state of themetamagnetic material layer from the magnetic state to the non-magneticstate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a random access memory device includingmagnetoresistive memory cells of the present disclosure in an arrayconfiguration.

FIG. 2 schematically illustrates a first exemplary tunnelingmetamagnetic resistance (TMMR) memory cell according to a firstembodiment of the present disclosure.

FIG. 3A schematically illustrates a first configuration of a secondexemplary tunneling metamagnetic resistance (TMMR) memory cell accordingto a second embodiment of the present disclosure.

FIG. 3B schematically illustrates a second configuration of the secondexemplary tunneling metamagnetic resistance (TMMR) memory cell accordingto the second embodiment of the present disclosure.

DETAILED DESCRIPTION

As discussed above, the embodiments of the present disclosure aredirected to tunneling metamagnetic resistance memory devices employingelectrical field-induced switching and methods of operating the same,the various aspects of which are described below.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are employed merely to identify similar elements, and differentordinals may be employed across the specification and the claims of theinstant disclosure. The term “at least one” element refers to allpossibilities including the possibility of a single element and thepossibility of multiple elements.

The same reference numerals refer to the same element or similarelement. Unless otherwise indicated, elements having the same referencenumerals are presumed to have the same composition and the samefunction. Unless otherwise indicated, a “contact” between elementsrefers to a direct contact between elements that provides an edge or asurface shared by the elements. If two or more elements are not indirect contact with each other or among one another, the two elementsare “disjoined from” each other or “disjoined among” one another. Asused herein, a first element located “on” a second element can belocated on the exterior side of a surface of the second element or onthe interior side of the second element. As used herein, a first elementis located “directly on” a second element if there exist a physicalcontact between a surface of the first element and a surface of thesecond element. As used herein, a first element is “electricallyconnected to” a second element if there exists a conductive pathconsisting of at least one conductive material between the first elementand the second element. As used herein, a “prototype” structure or an“in-process” structure refers to a transient structure that issubsequently modified in the shape or composition of at least onecomponent therein.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the first continuous structure.For example, a layer may be located between any pair of horizontalplanes between, or at, a top surface and a bottom surface of the firstcontinuous structure. A layer may extend horizontally, vertically,and/or along a tapered surface. A substrate may be a layer, may includeone or more layers therein, or may have one or more layer thereupon,thereabove, and/or therebelow.

Referring to FIG. 1, a schematic diagram is shown for a magnetoresistiverandom access memory (MRAM) device 500 including multiplemagnetoresistive memory cells 180 of embodiments of the presentdisclosure. In one embodiment, the magnetoresistive random access memorydevice 500 can contain a two-dimensional array or a three-dimensionalarray of magnetoresistive memory cell 180 of the embodiments of thepresent disclosure. As used herein, a “random access memory device”refers to a memory device containing memory cells that allow randomaccess, e.g., access to any selected memory cell upon a command forreading the contents of the selected memory cell.

The magnetoresistive random access memory device 500 can include amemory array region 550 containing an array of the respectivemagnetoresistive memory cells 180 located at the intersection of therespective word lines 30 and bit lines 90. The magnetoresistive randomaccess memory device 500 may also contain a row decoder 560 connected tothe word lines 30, a combination of a programming and sensing circuit570 (which can include programming transistors, sense amplifiers, andother bit line control circuitry) connected to the bit lines 90, acolumn decoder 580 connected to the bit lines 90 through the programmingand sensing circuit 570, and a data buffer 590 connected to theprogramming and sensing circuit 570. Multiple instances of themagnetoresistive memory cells 180 are provided in an array configurationthat forms the magnetoresistive random access memory device 500. Assuch, each of the magnetoresistive memory cells 180 can be atwo-terminal device including a respective first electrode and arespective second electrode. It should be noted that the location andinterconnection of elements are schematic and the elements may bearranged in a different configuration. Further, a magnetoresistivememory cell 180 may be manufactured as a discrete device, i.e., a singleisolated device.

Referring to FIG. 2, a first exemplary magnetoresistive memory deviceaccording to a first embodiment of the present disclosure isillustrated. The first exemplary magnetoresistive memory cell 180 is atunneling metamagnetic resistance (TMMR) memory cell. The firstexemplary magnetoresistive memory device includes a magnetoresistivememory cell 180 that can function as a unit memory cell of the TMMRmagnetoresistive random access memory (TMMR MRAM) device 500 shown inFIG. 1. In this case, a plurality of magnetoresistive memory cells 180can be formed in an array configuration, which may be a two-dimensionalarray configuration or a three-dimensional array configuration.Alternatively, the magnetoresistive memory cell 180 illustrated in FIG.2 may be formed as a discrete memory device that is connected to arespective programming and sensing circuit. In other words, eachmagnetoresistive memory cell 180 may be connected to a respectiveprogramming and sensing circuit.

Each magnetoresistive memory cell 180 can include a first electrode 170,a second electrode 270, and a layer stack (280, 240) located between thefirst electrode 170 and the second electrode 270. The layer stack (280,240) includes a ferroelectric material layer 280 having a non-zeroferroelectric polarization (i.e., electric polarization), and includes ametamagnetic tunnel junction 240. The metamagnetic tunnel junction 240is shown in FIG. 2 as being located on the ferroelectric material layer280 (i.e., between the ferroelectric material layer 280 and the secondelectrode 270). However, in an alternative embodiment, the metamagnetictunnel junction 240 may be located under the ferroelectric materiallayer 280 (i.e., between the ferroelectric material layer 280 and thefirst electrode 170). The metamagnetic tunnel junction 240 can contact asurface of the ferroelectric material layer 280.

In one embodiment, each first electrode 170 can be located on arespective one of the word lines 30, and each second electrode 270 canbe located on a respective one of the bit lines 90. Alternatively, eachfirst electrode 170 can be located on a respective one of the bit lines90, and each second electrode 270 can be located on a respective one ofthe word lines 30. Alternatively, each electrode (170, 270) can be aportion of a respective word line 30 or bit line 90 rather than aseparate layer which contacts the respective word line or bit line. Theword lines 30 can be formed as a one-dimensional array of first metallines located at a first metal interconnect level and laterallyextending along a first horizontal direction, and the bit lines 90 canbe formed as a one-dimensional array of second metal lines located at asecond metal interconnect level and laterally extending along a secondhorizontal direction which may be non-parallel to (e.g., perpendicularto) the first horizontal direction. In one embodiment, each of the wordlines 30 and the bit lines 90 can comprise a metallic nitride linerincluding an optional conductive metallic nitride material (such as TiN,TaN, or WN) and a metallic fill material (such as Cu, W, Co, Ru, Mo, Al,etc.).

The first electrode 170 can comprise, and/or can consist essentially of,a conductive metallic nitride material or a non-magnetic metallicmaterial including at least one transition metal. The at least onetransition metal of the non-magnetic metallic material may be selectedfrom Cu, Cr, Ti, Ta, W, Mo, Al, Au and/or Ru. In this case, thesidewalls of the first electrode 170 may, or may not, be verticallycoincident with sidewalls of the metamagnetic tunnel junction 240. Inone embodiment, the thickness of the first electrode 170 may be in arange from 1 nm to 20 nm, such as from 2 nm to 10 nm, although lesserand greater thicknesses can also be employed.

Each layer stack (280, 240) can be formed, for example, by depositing aset of continuous material layers, and by patterning the set ofcontinuous material layer by a combination of lithographic patterningmethods and an anisotropic etch process or by a focused ion beam etchingprocess. Each layer stack (280, 240) can optionally include a set ofsidewalls that are vertically coincident with each other. As usedherein, two surfaces are “vertically coincident” if one of the twosurfaces overlie or underlie the other of the two surfaces and if thereexists a vertical plane that contains the two surfaces. The word lines30, a two-dimensional array of magnetoresistive memory cells 180, andthe bit lines 90 may be embedded within interconnect-level dielectricmaterial layers 20 that are formed over a substrate 10, which may be asemiconductor substrate, such as a silicon substrate, or an insulatingsubstrate, such as a sapphire substrate.

The ferroelectric material layer 280 can include, and/or can consistessentially of, at least one ferroelectric dielectric material such ashafnium oxide (such as hafnium oxide containing at least one dopantselected from Al, Zr, and Si and having a ferroelectricnon-centrosymmetric orthorhombic phase), zirconium oxide,hafnium-zirconium oxide, bismuth ferrite, barium titanate (such asBaTiO₃; BT), colemanite (such as Ca₂B₆O₁₁.5H₂O), bismuth titanate (suchas Bi₄Ti₃O₁₂), europium barium titanate, ferroelectric polymer,germanium telluride, langbeinite (such as M₂M′₂(SO₄)₃ in which M is amonovalent metal and M′ is a divalent metal), lead scandium tantalate(such as Pb(Sc_(x)Ta_(1-x))O₃), lead titanate (such as PbTiO₃; PT), leadzirconate titanate (such as Pb (Zr,Ti) O₃; PZT), lithium niobate (suchas LiNbO₃; LN), lanthanum aluminum oxide (LaAlO₃), polyvinylidenefluoride (CH₂CF₂), potassium niobate (such as KNbO₃), potassium sodiumtartrate (such as KNaC₄H₄O₆.4H₂O), potassium titanyl phosphate (such asKO₅PTi), sodium bismuth titanate (such as Na_(0.5)Bi_(0.5)TiO₃ orBi_(0.5)Na_(0.5)TiO₃), lithium tantalate (such as LiTaO₃ (LT)), leadlanthanum titanate (such as (Pb,La)TiO₃ (PLT)), lead lanthanum zirconatetitanate (such as (Pb,La)(Zr,Ti)O₃ (PLZT)), ammonium dihydrogenphosphate (such as NH₄H₂PO₄ (ADP)), or potassium dihydrogen phosphate(such as KH₂PO₄ (KDP)).

The metamagnetic tunnel junction 240 can include a metamagnetic materiallayer 236 located in contact with (e.g., located on in FIG. 2) theferroelectric material layer 280. As used herein, a “metamagneticmaterial” refers to a material having a non-magnetic state and amagnetic state. As used herein, a “metamagnetic tunnel junction” refersto a tunnel junction including a metamagnetic material layer, i.e., alayer consisting essentially of a metamagnetic material. The magneticstate of the metamagnetic material may be a ferromagnetic state having anon-zero net magnetization, a ferrimagnetic state, or anantiferromagnetic state. The non-magnetic state may be a paramagneticstate or a diamagnetic state. In one embodiment, the metamagneticmaterial layer 236 can comprise, and/or can consist essentially of, amaterial selected from Co, a FeRh alloy, an EuSe alloy, CrO₂, and/orlanthanum strontium manganite (“LSM”, e.g., La_(1-x)Sr_(x)MnO₃).

The insulating barrier layer 134 includes an insulating tunnel barriermaterial for forming a metamagnetic tunnel junction. The insulatingbarrier layer 134 can include, for example, magnesium oxide, aluminumoxide, strontium titanate, or a combination thereof. The thickness ofthe insulating barrier layer 134 can be sufficiently thin to permittunneling current to flow through it, such as a thickness in a rangefrom 0.5 nm to 2 nm, such as from 0.7 nm to 1.2 nm, although lesser andgreater thicknesses can also be employed.

The metallic material layer 232 can include any metallic material thatdoes not affect the transition between the magnetic state and thenon-magnetic state within the metamagnetic material layer 236. In oneembodiment, the metallic material layer 232 includes a non-ferromagneticmetallic material, i.e., a metallic material that does not have aferromagnetic state. In one embodiment, the metallic material layer 232includes a non-magnetic metallic material, i.e., a metallic materialthat does not have a ferromagnetic state, a ferrimagnetic state, or anantiferromagnetic state. For example, the metallic material layer 232can include Cu, Cr, Ti, Ta, Au and/or Ru. The thickness of the metallicmaterial layer 232 may be in a range from 1 nm to 10 nm, such as from 2nm to 5 nm, although lesser and greater thicknesses can also beemployed.

In one embodiment, the second electrode 270 may comprise a non-magneticcapping layer located on the metallic material layer 232. For example,if the metallic material layer 232 comprises Cr, then the capping layercan comprise, and/or can consist essentially of, Ru and/or Ta.Alternatively, the second electrode 270 may comprise at least onenon-magnetic transition metal, which may be selected from Cu, Cr, Ti,Ta, W, Mo, Al, Au and/or Ru.

The sidewalls of the second electrode 270 may, or may not, be verticallycoincident with sidewalls of the metamagnetic tunnel junction 240. Thethickness of the second electrode 270 may be in a range from 1 nm to 20nm, such as from 2 nm to 10 nm, although lesser and greater thicknessescan also be employed.

In an alternative embodiment, the first electrode 170 may comprise aportion of a word line 30 that has an areal overlap with the area of themetamagnetic tunnel junction 240 and may directly contact a surface ofthe ferroelectric material layer 280. Additionally or alternatively, thesecond electrode 270 may comprise a portion of a bit line 90 that has anareal overlap with the area of the metamagnetic tunnel junction 240 andmay directly contact a surface of the metallic material layer 232.

A magnetoresistive memory device 180 of the first embodiment includes afirst electrode 170, a second electrode 270 and a layer stack (240, 280)located between the first electrode and the second electrode, the layerstack comprising a ferroelectric material layer 280 and a metamagnetictunnel junction 240. The metamagnetic tunnel junction 240 comprises ametamagnetic material layer 236, a metallic material layer 232, and aninsulating barrier layer 134 located between the metallic material layerand the metamagnetic material layer.

According to an embodiment of the present disclosure, the metamagneticmaterial layer 136 may directly contact the ferroelectric material layer280 and the insulating barrier layer 134.

According to an embodiment of the present disclosure, the metamagnetictunnel junction 240 has different tunneling magnetoresistance between afirst state in which the metamagnetic material layer 236 is in thenon-magnetic state and a second state in which the metamagnetic materiallayer 236 is in the magnetic state. The mechanism for the differenttunneling magnetoresistance between the first state and the second statecan be caused by constriction of tunneling current by availableelectronic surface states at the interface between the metamagneticmaterial layer 236 and the insulating barrier layer 134. In oneembodiment, the metamagnetic material of the metamagnetic material layer236 can have a variable surface density of states at an interface withthe insulating barrier layer 134 that changes between the non-magneticstate of the metamagnetic material and the magnetic state of themetamagnetic material. In one embodiment, the metamagnetic tunneljunction 240 has a variable tunneling resistance that increases with adecrease in the variable surface density of states of the metamagneticmaterial of the metamagnetic material layer 236 at the interface withthe insulating barrier layer 134.

In one embodiment, the magnetic state of the metamagnetic material layer236 comprises a ferromagnetic state, a ferrimagnetic state, or anantiferromagnetic state, and the non-magnetic state of the metamagneticmaterial layer 236 comprises a paramagnetic state of a diamagneticstate. In one embodiment, the metamagnetic material layer 236 has afirst surface density of states in the magnetic state, and themetamagnetic material layer 236 has a second surface layer density inthe non-magnetic state. The ratio of the first surface density of statesto the second surface state density can be at a level that can bedetected by a sensing circuit connected to the magnetoresistive memorycell 180. For example, the ratio of the first surface density of statesto the second surface density of states may be in a range from 0.1 to0.95, such as from 0.2 to 0.75, or may be in a range from 1.05 to 10,such as from 1.33 to 5. The ratio of the first surface density of statesto the second surface density of states depends on the nature of thechanges in the surface electronic states at the interface between themetamagnetic material layer 236 and the insulating barrier layer 134.

In one embodiment, the ferroelectric material layer 280 comprises twobistable polarization directions for the non-zero electric polarization.Alignment of the non-zero electric polarization along one of the twobistable polarization directions induces the magnetic state in themetamagnetic material layer 236, and alignment of the non-zero electricpolarization along another of the two bistable polarization directionsinduces the non-magnetic state in the metamagnetic material layer 236.In one embodiment, the two bistable polarization directions of thenon-zero electric polarization of the ferroelectric material layer 280can be opposite directions, i.e., can be antiparallel to each other. Inone embodiment, the two bistable polarization directions can be at anon-zero angle with respective to the interface between theferroelectric material layer 280 and the metamagnetic material layer236. In one embodiment, the two bistable polarization directions can beat an angle in a range from 30 degrees to 90 degrees, such as from 60degrees to 90 degrees, with respective to the interface between theferroelectric material layer 280 and the metamagnetic material layer236.

In one embodiment, the first exemplary magnetoresistive memory devicecan include a programming circuitry comprises a row decoder 560 and aprogramming and sensing circuit 570 that are configured to apply a firstprogramming voltage pulse of a first polarity between the firstelectrode 170 and the second electrode 270 to program the metamagneticmaterial layer 236 into the magnetic state, and to apply a secondprogramming pulse of a second polarity that is the opposite of the firstpolarity between the first electrode 170 and the second electrode 270 toprogram the metamagnetic material layer 236 into the non-magnetic state.Specifically, the programming voltage pulses may change the polarizationdirection of the ferroelectric material layer 280. The polarizationdirection of the ferroelectric material layer 280 then causes themetamagnetic material layer 236 to change between the magnetic state andthe non-magnetic state or vice-versa. In one embodiment, the firstpolarity can provide a more positive voltage to the first electrode 170relative to the second electrode 270 and the second polarity can providea more negative voltage to the first electrode 170 relative to thesecond electrode 270. In another embodiment, the first polarity canprovide a more negative voltage to the first electrode 170 relative tothe second electrode 270 and the second polarity can provide a morepositive voltage to the first electrode 170 relative to the secondelectrode 270.

Thus, an applied voltage may be used to change the state of themetamagnetic material layer 236 without generating a tunneling currentthrough the junction 240. This reduces the amount of power required tochange the resistivity of the memory cell 180. The correspondencebetween the specific polarization direction of the ferroelectricmaterial layer 280 and the magnetic or non-magnetic state of themetamagnetic material layer 236 depends on particular materials oflayers 280 and 236.

In an illustrative example, the ferroelectric material layer 280includes HfO₂ or BaTiO₃ and has a thickness in a range from 1 nm to 5nm, the metamagnetic material layer 236 includes a cobalt layer or anFeRh layer having a thickness in a range from 1 nm to 3 nm, theinsulating barrier layer 134 includes a magnesium oxide layer having athickness in a range from 1 nm to 3 nm, and the metallic material layer232 includes a TiN layer or a tungsten layer having a thickness in arange from 2 nm to 5 nm. In this case, the first programming pulse mayhave a magnitude in a range from 0.5 V to 3.0 V, and the secondprogramming pulse may have a magnitude in a range from −0.5 V to −3.0 V.The duration of each of the first programming pulse and the secondprogramming pulse may be in a range from 0.1 ns to 100 ns, such as from1 ns to 10 ns, although lesser and greater pulse durations can also beemployed. The programming and sensing circuit 570 can be configured toapply a sensing pulse having a magnitude in a range from 0.1 V to 0.5 V.

In one embodiment, a magnetoresistive random access memory is provided,which includes a two-dimensional array of instances of the firstexemplary magnetoresistive memory cell 180, word lines 30 electricallyconnecting a respective subset of the first electrodes 170 of thetwo-dimensional array, bit lines 90 electrically connecting a respectivesubset of the second electrodes 270 of the two-dimensional array, a rowdecoder 560 and a programming and sensing circuit 570 connected to theword lines 30, and the bit lines 90 and configured to program one ormore of the first exemplary magnetoresistive memory cells 180.

In one embodiment, the first exemplary magnetoresistive memory device ofFIG. 2 can be programmed by applying a first polarity programmingvoltage to the first electrode 170 relative to the second electrode 270in a first programming step to switch a state of the metamagneticmaterial layer 236 from the non-magnetic state to the magnetic state,and/or by applying a second polarity programming voltage having anopposite polarity of the first polarity programming voltage the firstelectrode 170 relative to the second electrode 270 in a secondprogramming step to switch the state of the metamagnetic material layer236 from the magnetic state to the non-magnetic state.

In one embodiment, the first polarity programming voltage changes apolarization direction of the ferroelectric material layer from a firstdirection to a second direction, which causes the metamagnetic materiallayer state to change from the non-magnetic state to the magnetic state.The second polarity programming voltage changes the polarizationdirection of the ferroelectric material layer from the second directionto the first direction, which causes the metamagnetic material layerstate to change from the magnetic state to the non-magnetic state. Inone embodiment, the state of the metamagnetic material layer 236 can besensed by measuring tunneling magnetoresistance of the metamagnetictunnel junction 240. The tunneling magnetoresistance can change between40 and 150 percent between the two states of the metamagnetic materiallayer 236.

Referring to FIGS. 3A and 3B, second exemplary tunneling metamagneticresistance (TMMR) memory cells 180 according to the second embodiment ofthe present disclosure are illustrated. FIG. 3A illustrates a firstconfiguration of the second exemplary structure, and FIG. 3B illustratesa second configuration of the second exemplary structure which bothinclude a multiferroic material layer 380 in place of the ferroelectricmaterial layer 280. The second exemplary magnetoresistive memory devicecan include a magnetoresistive memory cell 180 that can function as aunit memory cell of the magnetoresistive random access memory device500. In this case, a plurality of magnetoresistive memory cells 180 canbe formed in an array configuration, which may be a two-dimensionalarray configuration or a three-dimensional array configuration.Alternatively, the magnetoresistive memory cells 180 illustrated inFIGS. 3A and 3B may be formed as a discrete memory device that isconnected to a respective programming and sensing circuit. In otherwords, each magnetoresistive memory cell 180 may be connected to arespective programming and sensing circuit.

Each magnetoresistive memory cell 180 can include a first electrode 170,a second electrode 270, and a layer stack (380, 340) located between thefirst electrode 170 and the second electrode 270. The first and secondelectrodes (170, 270) and the word lines and bit lines (30, 90) may bethe same as in the first embodiment and will not be described in moredetail below.

The layer stack (380, 340) includes a multiferroic material layer 380including a multiferroic material, and includes a metamagnetic tunneljunction 340. As used herein, a “multiferroic” material refers to amaterial that exhibits at least two of a ferromagnetic-type order (suchas ferromagnetism, antiferromagnetism, or ferrimagnetism),ferroelectricity, and ferroelasticity. As used herein, a“magnetoelectric multiferroic” refers to a material that exhibits theferromagnetic-type order and ferroelectricity. A change in totalmagnetization is coupled to a change in total electric polarization in amagnetoelectric multiferroic, and thus, a magnetic transition can becoupled to a change in the electric polarization and vice versa.

The metamagnetic tunnel junction 340 is shown in FIGS. 3A and 3B asbeing located on the multiferroic material layer 380 (i.e., between themultiferroic material layer 380 and the second electrode 270). However,in an alternative embodiment, the metamagnetic tunnel junction 340 maybe located under the multiferroic material layer 380 (i.e., between themultiferroic material layer 280 and the first electrode 170). Themetamagnetic tunnel junction 340 can contact a surface of themultiferroic material layer 380.

The metamagnetic tunnel junction 340 comprises a metamagnetic materiallayer 236 located in contact with the multiferroic material layer 380and comprising a material having a non-magnetic state and a magneticstate, an insulating barrier layer 134 located on the metamagneticmaterial layer 236, and a reference magnetization layer 132 located onthe insulating barrier layer 134 and having a fixed magnetizationdirection. The metamagnetic tunnel junction 340 can contact a surface ofthe multiferroic material layer 380.

In one embodiment, the multiferroic material layer 380 can include,and/or can consist essentially of, a magnetoelectric multiferroicmaterial that exhibits a ferromagnetic-type order and ferroelectricity.Thus, the multiferroic material layer 380 has a non-zero electricpolarization. A change in total magnetization is coupled to a change intotal electric polarization in a magnetoelectric multiferroic, and thus,a magnetic transition can be coupled to a change in the electricpolarization and vice versa.

In one embodiment, the multiferroic material layer 380 comprises, and/orconsists essentially of, a multiferroic material in which the relativeorientation between the non-zero electric polarization of themultiferroic material layer 380 and the net magnetization of themultiferroic material layer 380 is invariant upon reversal of adirection of the non-zero electric polarization of the multiferroicmaterial layer 380. In one embodiment, the magnetization of themultiferroic material layer 380 has a bistable configuration in which afirst magnetization direction and a second magnetization direction arestable directions for the magnetization of the multiferroic materiallayer, and the second magnetization direction is antiparallel to thefirst magnetization direction.

In an illustrative example, the relative orientation between thenon-zero electric polarization of BiFeO₃ multiferroic material and thenet magnetization of BiFeO₃ is invariant upon reversal of a direction ofthe non-zero electric polarization of BiFeO₃, In one embodiment, themultiferroic material layer 380 may comprise a material selected fromBiFeO₃, h-YMnO₃, BaNiF₄, PbVO₃, BiMnO₃, LuFe₂O₄, HoMn₂O₅, h-HoMnO₃,h-ScMnO₃, h-ErMnO₃, h-TmMnO₃, h-YbMnO₃, h-LuMnO₃, K₂SeO₄, Cs₂CdI₄,ThMnO₃, Ni₃V₂O₈, MnWO₄, CuO, ZnCr₂Se₄, LiCu₂O₂, and Ni₃B₇O₁₃I. Thethickness of the multiferroic material layer 380 can be in a range from1 nm to 10 nm, such as from 2 nm to 5 nm, although lesser and greaterthicknesses can also be employed.

The metamagnetic tunnel junction 340 can include a metamagnetic materiallayer 236 located in contact with (e.g., located on) the multiferroicmaterial layer 380. In one embodiment, the magnetic state of themetamagnetic material of the metamagnetic tunnel junction 340 may be aferromagnetic state having a non-zero net magnetization. Thenon-magnetic state may be a paramagnetic state or a diamagnetic state.In one embodiment, the metamagnetic material layer 236 can comprise,and/or can consist essentially of, a material selected from Co, a FeRhalloy, an EuSe alloy, CrO₂, and/or LSM.

The insulating barrier layer 134 includes an insulating barrier materialfor forming a metamagnetic tunnel junction. The insulating barrier layer134 can include, for example, magnesium oxide, aluminum oxide, strontiumtitanate, or a combination thereof. The thickness of the insulatingbarrier layer 134 can be in a range from 0.5 nm to 2.0 nm, such as from0.7 nm to 1.2 nm, although lesser and greater thicknesses can also beemployed.

The reference magnetization layer 132 can include a ferromagneticmaterial having perpendicular magnetic anisotropy. The referencemagnetization layer 132 includes a material that can provide highperpendicular magnetic anisotropy. Thus, the magnetization direction ofthe reference magnetization layer 132 is along a vertical direction,i.e., the direction that is perpendicular to the interfaces betweencontacting layers within metamagnetic tunnel junction 340. Theferromagnetic material of the reference magnetization layer 132 does notneed to generate any spin-polarized current.

In one embodiment, the reference magnetization layer 132 comprises amaterial selected from a FePt alloy, a FePd alloy, a CoPt alloy, a Pt/Comultilayer stack, a Co/Ag multilayer stack, a Co/Cu multilayer stack, aCo/Ni multilayer stack, a (Pt/Co/Pt)/Pd multilayer stack, a(Pt/Co/Pt)/Ag multilayer stack, a (Pt/Co/Pt)/Cu multilayer stack, a(Pt/Co/Pt)/Ni multilayer stack, and a Co/(Pt/Pd) multilayer stack. In anillustrative example, the reference magnetization layer 132 can includeL1₀ alloys of FePt, FePd, or CoPt disclosed in Journal of AppliedPhysics 111, 07A708 (2012). The FePt alloy, the FePd alloy, and the CoPtalloy can have a magnetic anisotropy constant of 6.6×10⁷ erg/cm³,1.8×10⁷ erg/cm³, and 4.9×10⁷ erg/cm³, respectively. In anotherillustrative example, the reference magnetization layer 132 can includePt/Co multilayers, Co/Ag multilayers, Co/Cu multilayers, or Co/Nimultilayers, or can include (Pt/Co/Pt)/Pd multilayers, (Pt/Co/Pt)/Agmultilayers, (Pt/Co/Pt)/Cu multilayers, or (Pt/Co/Pt)/Ni multilayersdisclosed in IEEE Transaction on Magnetics 31, 3337 (1995). In yetanother illustrative example, the reference magnetization layer 132 caninclude Co/(Pt/Pd) multilayers or Co/(Pd/Pt) multilayers disclosed inJournal of Applied Physics 77, 3995 (1995). Alternatively, the referencemagnetization layer 132 can include a Fe layer, a Co layer, a Ni layer,a CoFeB layer, a CoFe layer, a Co/Ni multilayer structure or a Co/Ptmultilayer structure. The reference magnetization layer 132 can have athickness of 2 to 10 nm, such as 3 to 6 nm.

In the first configuration of the second exemplary structure, asynthetic antiferromagnet (SAF) structure 320 may be provided. In thiscase, the SAF structure 320 comprises a layer stack including, from oneside to another, the reference magnetization layer 132, anantiferromagnetic coupling layer 114, and a fixed magnetization layer112.

The reference magnetization layer 132 can include any soft ferromagneticmaterial, such as CoFe or CoFeB. The antiferromagnetic coupling layer114 can include an antiferromagnetic coupling material, such asruthenium, iridium, iridium-manganese alloy or a multilayer stack ofcobalt and platinum layers, and can have a thickness in a range from 0.5nm to 2 nm. The thickness of the antiferromagnetic coupling layer 114can be optimized to maximize antiferromagnetic coupling between thereference magnetization layer 132 and the fixed magnetization layer 112.

The fixed magnetization layer 112 is spaced from the referencemagnetization layer 132, and can include any material that may beemployed for the reference magnetization layer 132. The thickness of thefixed magnetization layer 112 can be in a range from 2 to 10 nm, such as3 to 6 nm. The antiferromagnetic coupling layer 114antiferromagnetically couples the fixed magnetization of referencemagnetization layer 132 to the magnetization of the fixed magnetizationlayer 112. Thus, the fixed magnetization of reference magnetizationlayer 132 is antiparallel to the magnetization of the fixedmagnetization layer 112.

In the second configuration of the second exemplary structure shown inFIG. 3B, any hard magnetic material that can provide high perpendicularmagnetic anisotropy can be employed for the reference magnetizationlayer 132. In this embodiment, the SAF structure 320 is omitted.

In one embodiment, the second electrode 270 may comprise capping layerlocated on the metallic material layer 232. In this case, the secondelectrode 270 can comprise, and/or can consist essentially of, Ru and/orTa. Alternatively, the second electrode 270 may comprise at least onenon-magnetic transition metal, which may be selected from Cu, Cr, Ti,Ta, W, Mo, Al, Au and/or Ru.

In the first configuration illustrated in FIG. 3A, the second electrode270 can contact the fixed magnetization layer 112 of the SAF structure320. In the second configuration illustrated in FIG. 3B, the secondelectrode 270 can contact the reference magnetization layer 132.

In an alternative embodiment, the first electrode 170 may comprise aportion of a word line 30 that has an areal overlap with the area of themetamagnetic tunnel junction 340 and directly contacts a surface of themultiferroic material layer 380. Additionally or alternatively, thesecond electrode 270 may comprise portion of a bit line 90 that has anareal overlap with the area of the metamagnetic tunnel junction 340 anddirectly contacts a surface of the metallic material layer 232.

According to an embodiment of the present disclosure, the multiferroicmaterial layer 380 has a non-zero electric polarization that is coupledto the magnetization of the multiferroic material layer 380. Aprogramming voltage pulse applied between the first and the secondelectrodes (170, 270) changes the electric polarization direction of themultiferroic material layer 380, which causes a corresponding change inthe magnetization direction of the multiferroic material layer 380. Inone embodiment, the multiferroic material layer 380 is magneticallycoupled to the metamagnetic material layer 236, and a change in themagnetization direction in the multiferroic material layer 380 induces atransition between the magnetic state and the non-magnetic state of themetamagnetic material layer 236. Thus, the resistivity state of themetamagnetic tunnel junction 340 may be changed by an appliedprogramming voltage pulse alone without generating a tunneling currentthrough the junction 340.

In summary, the ferroelectric nature of the multiferroic material willinduce ferromagnetism in metamagnetic material. Furthermore, themagnetic nature of the multiferroic materials will align theferromagnetic spins of the magnetic state of metamagnetic material inone of two directions. Thus, the magnetization direction of themultiferroic material layer 380 is coupled to the direction of thenon-zero electric polarization of the multiferroic material layer 380. Achange in the direction of the non-zero electric polarization of themultiferroic material layer 380 induces a change in the magnetizationdirection in the multiferroic material layer 380. The direction of thenon-zero electric polarization of the multiferroic material layer 380may be changed by an external voltage applied between the firstelectrode 170 and the second electrode 270, which generates an electricfield along the vertical direction either upward or downward dependingon the polarity of the external voltage. Upon application of asufficient voltage in either direction, the vertical component of thenon-zero electric polarization of the multiferroic material layer 380aligns to the vertical direction of the electrical field within themultiferroic material layer 380. One of the first magnetizationdirection and the second magnetization direction of the multiferroicmaterial layer 380 induces the magnetic state within the metamagneticmaterial layer 236, and the other of the first magnetization directionand the second magnetization direction of the multiferroic materiallayer induces the non-magnetic state within the metamagnetic materiallayer 236. In one embodiment, the magnetic state comprises aferromagnetic state having a magnetization direction which is aligned inone of the first or the second magnetization directions. The specificdirections depend on the materials of layer 380 and 236.

A magnetoresistive memory device 180 of the second embodiment includes afirst electrode 170, a second electrode 270, and a layer stack (340,380) located between the first electrode and the second electrode, thelayer stack comprising a multiferroic material layer 380 and ametamagnetic tunnel junction 340. The metamagnetic tunnel junction 340comprises a metamagnetic material layer 236, a reference magnetizationlayer 132, and an insulating barrier layer 134 located between thereference magnetization layer and the metamagnetic material layer.

In one embodiment, the metamagnetic material layer 236 physicallycontacts the multiferroic material layer 280 and the insulating barrierlayer 134.

In one embodiment, the magnetic state of the metamagnetic material layer236 comprises a ferromagnetic state of the metamagnetic material layer236. In one embodiment, the reference magnetization layer 132 comprisesa fixed magnetization direction that is oriented along a direction thatis antiparallel to the vertical component of a magnetization directionof the ferromagnetic state of the metamagnetic material layer 236.

Generally, a tunnel junction with two ferromagnetic material layers withantiferromagnetic alignment of magnetizations provides a highertunneling resistance than a tunnel junction in which one of the twoferromagnetic material layers is replaced with a non-magnetic metallicmaterial having the same electrical conductivity as the replacedferromagnetic material layer. The metamagnetic tunnel junction 340 has afirst state (which is a low resistance state) in which the metamagneticmaterial layer 236 is in a non-magnetic state. The metamagnetic tunneljunction 340 has a second state (which is a high resistance state) inwhich the metamagnetic material layer 236 is in a ferromagnetic statewith a magnetization direction that is antiparallel to the magnetizationdirection of the reference magnetization layer 132.

The first state can provide a first tunneling magnetoresistance, and thesecond state can provide a second, higher tunneling magnetoresistance.In other words, the metamagnetic tunnel junction 340 can have the firsttunneling magnetoresistance while the metamagnetic material layer 236 isin the non-magnetic state, and the metamagnetic tunnel junction 340 canhave the second, higher tunneling magnetoresistance while themetamagnetic material layer 236 is in the magnetic state. In oneembodiment, the second tunneling magnetoresistance is at least 105% ofthe first tunneling magnetoresistance. For example, the ratio of thesecond tunneling magnetoresistance to the first tunnelingmagnetoresistance may be in a range from 1.05 to 6, such as from 2 to 6.

The second exemplary magnetoresistive memory cells 180 is a tunnelingmetamagnetic resistance (TMMR) memory cell. The magnetic state of themetamagnetic material layer 236 in the second exemplary magnetoresistivememory cell 180 may comprise a ferromagnetic state provided that themagnetic state of the metamagnetic material layer 236 can provide adifferent tunneling magnetoresistance than the non-magnetic state of themetamagnetic material layer 236 in the second exemplary magnetoresistivememory cell 180. Generally, the non-magnetic state of the metamagneticmaterial layer 236 comprises a paramagnetic state or a diamagneticstate.

In one embodiment, the second exemplary magnetoresistive memory devicecan include a programming circuit including a row decoder 560 and aprogramming and sensing circuit 570 that that is configured to apply afirst programming pulse of a first polarity between the first electrode170 and the second electrode 270 to program the metamagnetic materiallayer 236 into the magnetic state, and to apply a second programmingpulse of a second polarity that is the opposite of the first polarityacross the first electrode 170 and the second electrode 270 to programthe metamagnetic material layer 236 into the non-magnetic state. Thetransition between the magnetic state and the non-magnetic state of themetamagnetic material layer 236 can be induced through the change in thedirection of the non-zero electric polarization within the multiferroicmaterial layer 380 during application of the first programming pulse orthe second programming pulse.

In one embodiment, the first polarity can provide a more positivevoltage to the first electrode 170 relative to the second electrode 270and the second polarity can provide a more negative voltage to the firstelectrode 170 relative to the second electrode 270. In anotherembodiment, the first polarity can provide a more negative voltage tothe first electrode 170 relative to the second electrode 270 and thesecond polarity can provide a more positive voltage to the firstelectrode 170 relative to the second electrode 270.

In an illustrative example, the multiferroic material layer 380 includesBaTiO₃ and has a thickness in a range from 1 nm to 5 nm, themetamagnetic material layer 236 includes a cobalt layer or an FeRh layerhaving a thickness in a range from 1 nm to 3 nm, the insulating barrierlayer 134 includes a magnesium oxide layer having a thickness in a rangefrom 1 nm to 3 nm, and the reference magnetization layer 132 includes aCoFe layer or a CoFeB layer having a thickness in a range from 1 nm to 2nm. In this case, the first programming pulse may have a magnitude in arange from 0.5 V to 3 V, and the second programming pulse may have amagnitude in a range from −0.5 V to −3 V. The duration of each of thefirst programming pulse and the second programming pulse may be in arange from 0.1 ns to 100 ns, such as from 1 ns to 10 ns, although lesserand greater pulse durations can also be employed. The programming andsensing circuit 570 can be configured to apply a sensing pulse having amagnitude in a range from 0.1 V to 0.5 V.

In one embodiment, a magnetoresistive random access memory is provided,which includes a two-dimensional array of second exemplarymagnetoresistive memory cells 180, word lines 30 electrically connectinga respective subset of the first electrodes 170 of the two-dimensionalarray, bit lines 90 electrically connecting a respective subset of thesecond electrodes 270 of the two-dimensional array, and a programmingand sensing circuit 570 connected to the bit lines 90 and row decoders560 connected to the word lines 30 and configured to program arespective set of the exemplary magnetoresistive memory cells 180.

In the second embodiment, the second exemplary magnetoresistive memorydevices of FIGS. 3A and 3B can be programmed by applying a firstpolarity programming voltage to the first electrode 170 relative to thesecond electrode 270 in a first programming step to switch a state ofthe metamagnetic material layer 236 from the non-magnetic state to themagnetic state, and/or by applying a second polarity programming voltagehaving an opposite polarity of the first polarity programming voltagethe first electrode 170 relative to the second electrode 270 in a secondprogramming step to switch the state of the metamagnetic material layer236 from the magnetic state to the non-magnetic state. In oneembodiment, the state of the metamagnetic material layer 236 can besensed by measuring tunneling magnetoresistance of the metamagnetictunnel junction 240.

The various embodiments of the present disclosure provide amagnetoresistive memory device containing a metamagnetic material layer236, which is located a metamagnetic tunneling junction that provides atunneling metamagnetic resistance (TMMR) that changes with a change inthe magnetic state of the metamagnetic material layer 236. Theunderlying mechanism for the change in the TMMR may be a change in thesurface density of states at the interface between the metamagneticmaterial layer 236 and the insulating barrier layer 134 that accompaniesa magnetic phase transition within the metamagnetic material layer 236as in the case of the first exemplary TMMR memory device of FIG. 2 ofthe first embodiment. Alternatively, the underlying mechanism for thechange in the TMMR may be a change in the tunneling efficiency ofelectrons between the non-magnetic state of the metamagnetic materiallayer 236 in which the spin of the electrons does not play a role, andthe magnetic state of the metamagnetic material layer 236 in which theantiparallel alignment of magnetizations of the metamagnetic materiallayer 236 and the reference magnetization layer 132 decreases tunnelingefficiency of electrons as in the case of the second exemplary TMMRmemory device of FIGS. 3A and 3B of the second embodiment. In bothembodiments, only an applied voltage may be used to switch theresistance state of the memory cell without using a tunneling currentthrough the junction (240, 340). Thus, a lower switching energy may beused to deterministically program the TMMR MRAM memory cell with arelatively high TMR (e.g., 500% to 600%). In contrast, prior art STTMRAMs require higher switching energy and tunneling current forprogramming, while prior art VCMA MRAMs use an applied voltage toprogram the memory cells non-deterministically.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the disclosure is not so limited. It will occurto those of ordinary skill in the art that various modifications may bemade to the disclosed embodiments and that such modifications areintended to be within the scope of the disclosure. Where an embodimentemploying a particular structure and/or configuration is illustrated inthe present disclosure, it is understood that the present disclosure maybe practiced with any other compatible structures and/or configurationsthat are functionally equivalent provided that such substitutions arenot explicitly forbidden or otherwise known to be impossible to one ofordinary skill in the art. All of the publications, patent applicationsand patents cited herein are incorporated herein by reference in theirentirety.

What is claimed is:
 1. A magnetoresistive memory device, comprising: afirst electrode; a second electrode; and a layer stack located betweenthe first electrode and the second electrode, the layer stack comprisinga multiferroic material layer and a metamagnetic tunnel junction,wherein the metamagnetic tunnel junction comprises: a metamagneticmaterial layer; a reference magnetization layer; and an insulatingbarrier layer between the reference magnetization layer and themetamagnetic material layer; and at least one feature comprising: (a)first feature wherein: the multiferroic material layer has a non-zeroelectric polarization that is coupled to a magnetization of themultiferroic material layer; the magnetization of the multiferroicmaterial layer has a bistable configuration in which a firstmagnetization direction and a second magnetization direction are stabledirections for the magnetization of the multiferroic material layer; andthe second magnetization direction is antiparallel to the firstmagnetization direction; or (b) a second feature wherein the magneticstate of the metamagnetic material layer comprises a ferromagnetic stateof the metamagnetic material layer, and the non-magnetic state of themetamagnetic material layer comprises a paramagnetic state or adiamagnetic state; or (c) a third feature further comprising a syntheticantiferromagnet structure comprising: the reference magnetization layerwhich comprises a soft ferromagnetic layer; a fixed magnetization layerthat is spaced from the reference magnetization layer; and anantiferromagnetic coupling layer that antiferromagnetically couples amagnetization of reference magnetization layer to a magnetization of thefixed magnetization layer; or (d) a fourth feature further comprising aprogramming circuit that is configured: to apply a first programmingpulse of a first polarity across the first electrode and the secondelectrode to program the metamagnetic material layer into the magneticstate; and to apply a second programming pulse of a second polarity thatis an opposite of the first polarity across the first electrode and thesecond electrode to program the metamagnetic material layer into thenon-magnetic state.
 2. The magnetoresistive memory device of claim 1,wherein the metamagnetic material layer contacts the multiferroicmaterial layer and the insulating barrier layer.
 3. The magnetoresistivememory device of claim 1, wherein the at least one feature comprises thefirst feature.
 4. The magnetoresistive memory device of claim 3,wherein: the multiferroic material layer is magnetically coupled to themetamagnetic material layer; and a change in a magnetization directionin the multiferroic material layer induces a transition between themagnetic state and the non-magnetic state of the metamagnetic materiallayer.
 5. The magnetoresistive memory device of claim 4, wherein: themagnetization direction of the multiferroic material layer is coupled toa direction of the non-zero electric polarization of the multiferroicmaterial layer; and a change in the direction of the non-zero electricpolarization of the multiferroic material layer induces a change in themagnetization direction in the multiferroic material layer.
 6. Themagnetoresistive memory device of claim 4, wherein: one of the firstmagnetization direction and the second magnetization direction of themultiferroic material layer induces the magnetic state within themetamagnetic material layer, wherein the magnetic state comprises aferromagnetic state having a magnetization direction which is aligned inone of the first or the second magnetization directions; and another ofthe first magnetization direction and the second magnetization directionof the multiferroic material layer induces the non-magnetic state withinthe metamagnetic material layer.
 7. The magnetoresistive memory deviceof claim 1, wherein the at least one feature comprises the secondfeature.
 8. The magnetoresistive memory device of claim 7, wherein thereference magnetization layer has a fixed magnetization direction thatis oriented along a direction that is antiparallel to a verticalcomponent of a magnetization of the ferromagnetic state of themetamagnetic material layer.
 9. The magnetoresistive memory device ofclaim 8, wherein: the metamagnetic tunnel junction has a first tunnelingmagnetoresistance while the metamagnetic material layer is in thenon-magnetic state; and the metamagnetic tunnel junction has a secondtunneling magnetoresistance greater than the first magnetoresistancewhile the metamagnetic material layer is in the magnetic state.
 10. Themagnetoresistive memory device of claim 1, wherein the at least onefeature comprises the third feature.
 11. The magnetoresistive memorydevice of claim 1, wherein the reference magnetization layer comprises ahard magnetic layer.
 12. The magnetoresistive memory device of claim 1,wherein the multiferroic material layer comprises a material selectedfrom BiFeO₃, h-YMnO₃, BaNiF₄, PbVO₃, BiMnO₃, LuFe₂O₄, HoMn₂O₅, h-HoMnO₃,h-ScMnO₃, h-ErMnO₃, h-TmMnO₃, h-YbMnO₃, h-LuMnO₃, K₂SeO₄, Cs₂CdI₄,TbMnO₃, Ni₃V₂O₈, MnWO₄, CuO, ZnCr₂Se₄, LiCu₂O₂, or Ni₃B₇O₁₃I.
 13. Themagnetoresistive memory device of claim 1, wherein the metamagneticmaterial layer comprises a material selected from Co, a FeRh alloy, anEuSe alloy, CrO₂, or LaSrMnO₃.
 14. The magnetoresistive memory device ofclaim 1, wherein the insulating barrier layer comprises a materialselected from magnesium oxide, aluminum oxide, strontium titanate, or acombination thereof.
 15. The magnetoresistive memory device of claim 1,wherein the at least one feature comprises the fourth feature.
 16. Amagnetoresistive random access memory device, comprising: atwo-dimensional array of instances of the magnetoresistive memory devicecomprising: a first electrode; a second electrode; and a layer stacklocated between the first electrode and the second electrode, the layerstack comprising a multiferroic material layer and a metamagnetic tunneljunction, wherein the metamagnetic tunnel junction comprises: ametamagnetic material layer; a reference magnetization layer; and aninsulating barrier layer between the reference magnetization layer andthe metamagnetic material layer; and word lines electrically connectedto a respective subset of the first electrodes of the two-dimensionalarray; bit lines electrically connected to a respective subset of thesecond electrodes of the two-dimensional array; and a programmingcircuit connected to the bit lines and the word lines and configured toprogram the magnetoresistive memory device.
 17. A method of operating amagnetoresistive memory device comprising: a first electrode; a secondelectrode; and a layer stack located between the first electrode and thesecond electrode, the layer stack comprising a multiferroic materiallayer and a metamagnetic tunnel junction, wherein the metamagnetictunnel junction comprises: a metamagnetic material layer; a referencemagnetization layer; and an insulating barrier layer between thereference magnetization layer and the metamagnetic material layer, themethod comprising: applying a first polarity programming voltage to thefirst electrode relative to the second electrode in a first programmingstep to switch a state of the metamagnetic material layer from thenon-magnetic state to the magnetic state; and applying a second polarityprogramming voltage having an opposite polarity of the first polarityprogramming voltage the first electrode relative to the second electrodein a second programming step to switch the state of the metamagneticmaterial layer from the magnetic state to the non-magnetic state. 18.The method of claim 17, wherein: the first polarity programming voltagechanges a polarization direction of the multiferroic material layer froma first direction to a second direction, which causes the metamagneticmaterial layer state to change from the non-magnetic state to themagnetic state; and the second polarity programming voltage changes thepolarization direction of the multiferroic material layer from thesecond direction to the first direction, which causes the metamagneticmaterial layer state to change from the magnetic state to thenon-magnetic state.
 19. The method of claim 18, further comprisingdetermining the state of the metamagnetic material layer by measuringtunneling magnetoresistance of the metamagnetic tunnel junction.